1. Field of the Invention
The invention is based on a burner.
2. Brief Description of the Related Art
Premix burners that are operated based on the concept of lean premix combustion, have low pollutant emissions but also a clearly restricted stability and operating range. These restrictions are caused by flashback into the mixing zone of the burner and lift-off and extinguishing of the premix flame as well as by thermo-acoustic oscillations. The stability range during conventional operation of a premix burner is expanded by using pilot injection that is especially used in the lower load range. However, already small amounts of 10% pilot gas, for example, can result in clearly increased pollutant emissions since the pilot flames work in diffusion operation. Pilot injection is turned off or reduced to the largest degree possible in the upper load range in order to guarantee low pollutant emissions.
In the case of the premix burner disclosed in EP 0 321 809 A1, a so-called double-cone burner, the pilot burner is realized by injecting fuel in the center of the vortex body, called double cone in this case. The gas that flows into the interior of the double-cone burner burns in a flame that is stabilized deep inside the interior space of the burner.
EP 0 704 657 A2 discloses another premix burner in which the pilot burner is realized by the fuel flowing from an annular gas channel with exit holes that are tilted to the outside into the outside backflow zone of the combustion chamber following the burner outlet. The gas that flows out burns in a flame that is stabilized by the cross section jump on the burner outlet.
Neither the embodiment of the external pilot system according to EP 0 704 657 A2 nor the internal pilot system according to EP 0 321 809 B1 can ensure optimum injection of the fuel across the entire load range in order to achieve the lowest possible pollutant emissions.
WO 01/96785 A1 discloses a burner with stepped premix gas injection in which a fuel lance extends into the vortex body. The fuel supply can be controlled so that exit openings on the fuel lance and exit openings on the vortex body can be fed, independent of each other, with premix gas. The exit openings on the vortex body and on the lance can be arranged so that no exit openings are arranged on the vortex body opposite the exit openings that are arranged on the lance.